Use registry in gdbarch

gdbarch implements its own registry-like approach.  This patch changes
it to instead use registry.h.  It's a rather large patch but largely
uninteresting -- it's mostly a straightforward conversion from the old
approach to the new one.

The main benefit of this change is that it introduces type safety to
the gdbarch registry.  It also removes a bunch of code.

One possible drawback is that, previously, the gdbarch registry
differentiated between pre- and post-initialization setup.  This
doesn't seem very important to me, though.

gdb/guile/scm-arch.c

@@ -41,7 +41,10 @@ static const char arch_smob_name[] = "gdb:arch";
 /* The tag Guile knows the arch smob by.  */
 static scm_t_bits arch_smob_tag;
 
-static struct gdbarch_data *arch_object_data = NULL;
+/* Use a 'void *' here because it isn't guaranteed that SCM is a
+   pointer.  */
+static const registry<gdbarch>::key<void, gdb::noop_deleter<void>>
+     arch_object_data;
 
 static int arscm_is_arch (SCM);
 
@@ -105,30 +108,28 @@ gdbscm_arch_p (SCM scm)
   return scm_from_bool (arscm_is_arch (scm));
 }
 
-/* Associates an arch_object with GDBARCH as gdbarch_data via the gdbarch
-   post init registration mechanism (gdbarch_data_register_post_init).  */
-
-static void *
-arscm_object_data_init (struct gdbarch *gdbarch)
-{
-  SCM arch_scm = arscm_make_arch_smob (gdbarch);
-
-  /* This object lasts the duration of the GDB session, so there is no
-     call to scm_gc_unprotect_object for it.  */
-  scm_gc_protect_object (arch_scm);
-
-  return (void *) arch_scm;
-}
-
 /* Return the <gdb:arch> object corresponding to GDBARCH.
    The object is cached in GDBARCH so this is simple.  */
 
 SCM
 arscm_scm_from_arch (struct gdbarch *gdbarch)
 {
-  SCM a_scm = (SCM) gdbarch_data (gdbarch, arch_object_data);
+  SCM arch_scm;
+  void *data = arch_object_data.get (gdbarch);
+  if (data == nullptr)
+    {
+      arch_scm = arscm_make_arch_smob (gdbarch);
 
-  return a_scm;
+      /* This object lasts the duration of the GDB session, so there
+	 is no call to scm_gc_unprotect_object for it.  */
+      scm_gc_protect_object (arch_scm);
+
+      arch_object_data.set (gdbarch, (void *) arch_scm);
+    }
+  else
+    arch_scm = (SCM) data;
+
+  return arch_scm;
 }
 
 /* Return the <gdb:arch> smob in SELF.
@@ -651,11 +652,3 @@ gdbscm_initialize_arches (void)
 
   gdbscm_define_functions (arch_functions, 1);
 }
-
-void _initialize_scm_arch ();
-void
-_initialize_scm_arch ()
-{
-  arch_object_data
-    = gdbarch_data_register_post_init (arscm_object_data_init);
-}

gdb/guile/scm-symbol.c

@@ -78,13 +78,14 @@ struct syscm_deleter
 
 static const registry<objfile>::key<htab, syscm_deleter>
      syscm_objfile_data_key;
-static struct gdbarch_data *syscm_gdbarch_data_key;
 
 struct syscm_gdbarch_data
 {
   /* Hash table to implement eqable gdbarch symbols.  */
   htab_t htab;
 };
+
+static const registry<gdbarch>::key<syscm_gdbarch_data> syscm_gdbarch_data_key;
 
 /* Administrivia for symbol smobs.  */
 
@@ -110,17 +111,6 @@ syscm_eq_symbol_smob (const void *ap, const void *bp)
 	  && a->symbol != NULL);
 }
 
-static void *
-syscm_init_arch_symbols (struct gdbarch *gdbarch)
-{
-  struct syscm_gdbarch_data *data
-    = GDBARCH_OBSTACK_ZALLOC (gdbarch, struct syscm_gdbarch_data);
-
-  data->htab = gdbscm_create_eqable_gsmob_ptr_map (syscm_hash_symbol_smob,
-						   syscm_eq_symbol_smob);
-  return data;
-}
-
 /* Return the struct symbol pointer -> SCM mapping table.
    It is created if necessary.  */
 
@@ -144,9 +134,14 @@ syscm_get_symbol_map (struct symbol *symbol)
   else
     {
       struct gdbarch *gdbarch = symbol->arch ();
-      struct syscm_gdbarch_data *data
-	= (struct syscm_gdbarch_data *) gdbarch_data (gdbarch,
-						      syscm_gdbarch_data_key);
+      struct syscm_gdbarch_data *data = syscm_gdbarch_data_key.get (gdbarch);
+      if (data == nullptr)
+	{
+	  data = syscm_gdbarch_data_key.emplace (gdbarch);
+	  data->htab
+	    = gdbscm_create_eqable_gsmob_ptr_map (syscm_hash_symbol_smob,
+						  syscm_eq_symbol_smob);
+	}
 
       htab = data->htab;
     }
@@ -817,12 +812,3 @@ gdbscm_initialize_symbols (void)
   domain_keyword = scm_from_latin1_keyword ("domain");
   frame_keyword = scm_from_latin1_keyword ("frame");
 }
-
-void _initialize_scm_symbol ();
-void
-_initialize_scm_symbol ()
-{
-  /* Arch-specific symbol data.  */
-  syscm_gdbarch_data_key
-    = gdbarch_data_register_post_init (syscm_init_arch_symbols);
-}